Abstract:
A superposed epoch analysis has been carried out of h′F values at Kodaikanal (10°14′N, 77°28′E, dip 3.0°N) pertaining to years of high sunspot activity using solar wind sector boundary passages past the earth as key days. It is found that there is a reduction in h′F values at 2000 LT 1 or 2 days after the sector boundary crossing. The amplitude of this effect which is noticed with both (+, −) and (−, +) sector boundary crossings is higher in equinoxes than in solstices. The response of the equatorial F region to sector boundary crossing seems to originate from perturbations of the equatorial east–west electric field in the post-sunset period associated with the enhancement in geomagnetic activity in the wake of sector boundary crossing.
